random voltage measuring question.

[bakerlite]

Just curios really
IS it ever possible that the chassis of an amp, would have a voltage reading on it like really small 0.2v?
more importantly what would be the correct way to test a chassis for voltage it may or may not be carrying? its not just as simple as placing meter probes in 2 seperate locations is it? well for some reason that wouldnt make sense to me. I thought you'd probe from the chassis to ground? except it is ground?
confused?

[HotBluePlates]

Just curios really
IS it ever possible that the chassis of an amp, would have a voltage reading on it like really small 0.2v?

It is possible, but it is more likely that your meter is displaying some small offset error.

Unless the chassis has relatively high resistivity/low conductivity (compared to typical chassis materials), it would take a VERY large current through the chassis to register even a small voltage difference between two points.

Remember, it takes 1 volt across 1 ohm to force 1 ampere of current through the resistance. So even if the resistance between the two points you're measuring is as much as 0.2Ω, there would need to be 1A flowing through that chassis to register 0.2v.

If, however, you're trying to find if your chassis is at some elevated voltage, it needs to be measured referred to some external reference point. That might be earth, through a stake driven in the ground which is ultimately connected to the 3rd wire of your outlet.

[sluckey]

IS it ever possible that the chassis of an amp, would have a voltage reading on it like really small 0.2v?

In reference to what?

Voltage is the difference in electrical potential between two points. Your chassis is one point. What is the other? If you mean dirt ground, sure there can be a voltage difference. There could be several connection points and maybe even 100 feet of copper wire between your chassis (which is bonded to ground) and the actual dirt you stick the other meter lead in. A big voltage means a bad connection(s) somewhere.

[bakerlite]

In reference to what?

Thanks folks - I guess that was my question but I didn't know how to word it. what is your reference when checking the chassis for stray voltage.

[HotBluePlates]

In reference to what?

Thanks folks - I guess that was my question but I didn't know how to word it. what is your reference when checking the chassis for stray voltage.

3rd prong of the outlet. Or maybe better, ANY outlet your gear is plugged in to.

Once upon a time, I was playing on stage and my amp was plugged into an outlet at the stage. The microphone was connected to a PA at the back of the seating area, and plugged in to an outlet near it. I had my hand on the guitar neck, walked up to the mic and got a zap that jumped out of the mic shell and hit me in the lip. I felt the jolt run down my left arm to the strings (which were grounded through the amp).

So in this case, the pair of outlets were no properly wired and referenced to the same "ground". When there's an error like this, the difference in references may be as much as 120v.

[PRR]

> the pair of outlets were no properly wired and referenced to the same "ground". When there's an error like this, the difference in references may be as much as 120v.

In a similar case, except the outlets _were_ "properly wired", I had a consistent 2V-3V between concert-hall stage and control booth. Couple hundred feet of conduit between them and various loads on multiple circuits across three phases. While 3V is hardly going to burn your lip, I did have to be aware of the ground difference.